1. Field of the Invention
The present invention relates to a semiconductor processing apparatus for performing semiconductor processing on an LCD (Liquid Crystal Display) substrate or a semiconductor wafer. The semiconductor processing means various processing steps performed to fabricate semiconductor devices on target substrates such as LCD substrates and semiconductor wafers.
2. Description of the Related Art
Conventionally, an LCD substrate manufacturing process, for example, is done by using a so-called multi-chamber vacuum processing apparatus which includes a plurality of vacuum processing vessels for performing predetermined processing steps such as etching and ashing on LCD substrates.
This multi-chamber vacuum processing apparatus has a transfer chamber adjacent to the individual processing chambers via gate valves and a load-lock chamber adjacent to the transfer chamber via a gate valve. The apparatus further has an external transfer mechanism such as a transfer arm and an internal transfer mechanism. The external transfer mechanism unloads LCD substrates one by one from a cassette, which stores a large number of LCD substrates and is placed in an outer atmosphere, and transfers these LCD substrates to the load-lock chamber. The internal transfer mechanism transfers the LCD substrates between the load-lock chamber and the processing chambers.
This LCD substrate vacuum processing apparatus is required to process as large a number of substrates as possible within a predetermined time period, i.e., required to increase the throughput as high as possible. The apparatus is a multi-chamber apparatus in order to improve the throughput by processing a plurality of substrates at the same time.
The transfer system is also naturally required to improve the throughput. To this end, a mechanism having two arms, i.e., upper and lower arms for directly supporting LCD substrates is used as the external transfer mechanism. That is, the upper arm supports an unprocessed substrate and the lower arm supports a processed substrate.
To load a processed substrate into the cassette and unload the next unprocessed substrate from the cassette, the lower arm first enters a predetermined slot in the cassette, the entire transfer arm moves down a predetermined distance to load the processed substrate onto a supporting portion in the slot, and then the lower arm once leaves the cassette. Subsequently, the entire transfer arm moves up and the upper arm enters a predetermined slot. The entire transfer arm further moves up to allow the upper arm to support the unprocessed substrate placed on a supporting portion of the slot. The upper arm is then retreated from the cassette.
Unfortunately, the reduction of the time is limited even with the use of the above substrate loading/unloading operation, and so it is required to further improve the throughput.
Also, the following procedure is used to access a susceptor in a vacuum processing chamber by using two arms, i.e., upper and lower arms as the internal transfer mechanism. First, an unprocessed substrate is placed on the upper arm and the transfer arms are advanced into the vacuum processing chamber. The lower arm is moved forward to receive a processed substrate from the susceptor and then moved backward, and the upper arm is moved forward to transfer the unprocessed substrate onto the susceptor.
Even when this substrate exchange operation is performed, however, there is a certain limit on the shortening of the time. Therefore, a further improvement of the throughput is demanded.